In semiconductor devices, due to the demand for achieving an increase in efficiency and saving more energy, there is a need to achieve a decrease in size, an increase in breakdown voltage, and a decrease in ON-resistance. For example, in a trench gate MOSFET (Metal Oxide Semiconductor Field Effect Transistor), in applying a voltage between the source and drain, the breakdown voltage is secured by depleting a drift layer. In semiconductor devices, a further improvement in the breakdown voltage is desired while maintaining a low ON-resistance.